A population study is being used to investigate the association between blood pressure change and the presence of glaucomatous-like visual field defects. Persons found to have visual field defects, carefully defined, are referred to a consulting ophthalmologist for definitive diagnosis. The study populati n involves persons in the current study of hypertension therapy, Hypertension Detection and Followup Program, sponsored by the National Heart and Lung Institute. These persons have been divided into three well-defined groups: normotensive, hypertensive with usual treatment, and hypertensive with intensive treatment. This population allows the investigation of the theoretical prediction, based on perfusion pressure theory, that lowering blood pressure may cause visual field defects. If true, the intensively treated group would have the greatest number of visual field defects. If the association between blood pressure reduction and visual field defects is significant, it could have serious implications for the current mode of therapy for systemic hypertension.